1. Field of the Invention
The present invention relates to sensing when a fluid in a reservoir reaches a critical level and, particularly, to the provision of an unambiguous fail-safe liquid level warning. More specifically, this invention is directed to a bi-stable liquid level warning device of reliable construction which is characterized by ease of installation and the provision of an easily interpreted read-out. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
2. Description of the Prior Art
A prior art liquid level warning device suitable for the same operating environments as the present invention is shown in U.S. Pat. Np. 5,425,271. The description of the prior art from U.S. Pat. No. 5,415,271 is incorporated herein by reference.
While the indicator of above-referenced U.S. Pat. No. 5,425,271 has enjoyed commercial success, there has remained a need for a level indicator which is characterized by bi-stable operation. Thus, in the device of U.S. Pat. No. 5,425,271, changes in the level of the liquid being monitored will result in rotation of the "flag" which provides the visual indication of liquid level. This rotation results from magnetic coupling between a pivotal member which is immersed in the liquid being monitored and the "flag". Between the limits of motion of the pivotal member, the rotation of the "flag", in effect, provides an analog read-out. Restated, in the patented device, an observer will make a judgment as to the level of the liquid being monitored by estimating the relative amounts of two colors, provided on different portions of the "flag", which are located behind a viewing window.
There are many applications where it is important to know, immediately and unambiguously, when the quantity of fluid in a reservoir has departed from a predetermined level. Thus, there has been a previously unsatisfied demand for a liquid level indicator which would be bi-stable in operation, i.e., the display of the indicator device would change from one state to a completely different state when the level of the liquid being monitored passes through a predetermined critical level.